As a common method of manufacturing a GaN-based semiconductor device, Japanese National Patent Publication No. 2001-501778 (PTL1) (corresponding to WO1998/014986) and O. B. Shchekin, et al., “High performance thin-film flip-chip InGaN—GaN light-emitting diodes,” APPLIED PHYSICS LETTERS 89, 071109 (2006), pp. 071109-1 to 071109-3 (NPL 1) disclose a method by which a GaN-based semiconductor layer is epitaxially grown on a sapphire substrate which is a base substrate, the GaN-based semiconductor layer is transferred onto a transfer support substrate or mounted on a mount substrate, and thereafter the sapphire substrate is removed from the GaN-based semiconductor layer by laser lift-off.